Howell Emma K, Baier Felix, Hoekstra Hopi E, Payseur Bret A
bioRxiv. 2025 Aug 24:2025.04.18.649517. doi: 10.1101/2025.04.18.649517.
Populations that colonize islands experience novel selective pressures, fluctuations in size, and changes to their connectivity. Owing to their unique geographic setting, islands can function as natural laboratories in which to examine the interactions between demographic history and natural selection replicated across isolated populations. We used whole genome sequences of wild-caught deer mice ( ) from two islands (Saturna and Pender) and one mainland location (Maple Ridge) in the Gulf Islands region of coastal British Columbia to investigate two primary determinants of genome-wide diversity: chromosomal inversions and non-equilibrium demographic history. We found that segregating inversions produce characteristic, large-scale distortions in allele frequencies and linkage disequilibrium that make it possible to identify and characterize them from short-read sequence data. Patterns of variation within and between karyotypes indicate that six inversion polymorphisms have been maintained by a shared history of balancing selection in both island and mainland populations. Whereas the estimated timing of contemporary population splits is consistent with the isolation of island populations following the Last Glacial Maximum, ancestral island and mainland lineages are inferred to have diverged much earlier. These aspects of demographic history suggest that shared inversions existed long ago in a common ancestor or spread via limited gene flow between ancestral island and mainland lineages. Our results raise the possibility that inversions segregating among Gulf Islands populations are on similar evolutionary trajectories, providing a contrast to previous findings in mainland and contributing to the emerging portrait of inversion evolution in this species.
殖民岛屿的种群会经历新的选择压力、种群数量波动以及连通性变化。由于其独特的地理环境，岛屿可作为天然实验室，用于研究人口历史与自然选择在孤立种群中的相互作用。我们利用从加拿大不列颠哥伦比亚省沿海海湾群岛地区的两个岛屿（萨图纳岛和彭德岛）以及一个大陆地点（枫树岭）捕获的野生鹿鼠的全基因组序列，来研究全基因组多样性的两个主要决定因素：染色体倒位和非平衡人口历史。我们发现，分离的倒位会在等位基因频率和连锁不平衡中产生特征性的大规模扭曲，从而使得从短读长序列数据中识别和表征它们成为可能。核型内部和之间的变异模式表明，六个倒位多态性在岛屿和大陆种群的平衡选择共同历史中得以维持。虽然当代种群分裂的估计时间与末次盛冰期后岛屿种群的隔离一致，但推断祖先岛屿和大陆谱系的分化要早得多。人口历史的这些方面表明，共享的倒位很久以前就存在于共同祖先中，或者是通过祖先岛屿和大陆谱系之间有限的基因流动传播的。我们的结果增加了这样一种可能性，即海湾群岛种群中分离的倒位处于相似的进化轨迹上，这与大陆上先前的研究结果形成对比，并有助于勾勒出该物种倒位进化的新图景。
